In a high-temperature solar heat application system, generally, the sunlight and heat are collected using a mirror. As the combination of a sunlight collecting apparatus and a heat receiving apparatus, there are two types of combinations, that is, a trough sunlight collecting type in which the sunlight collecting apparatus and the heat receiving apparatus are mechanically integrated with each other and are disposed at a position close to the ground and a tower collecting type in which the heat receiving apparatus is disposed on a tall tower and plural collecting reflection ray control mirrors called heliostats are disposed on the ground in the periphery of the heat receiving apparatus so that the heat receiving apparatus on the tower collects the sunlight.
In the tower sunlight collecting type which will be described in the present invention, in order to more improve the efficiency of a generation cycle in the case of an electric generation plant, a heat carrier, which is considered an increase in temperature, used for a heat-exchange operation in a sunlight collecting heat receiver has been developed.
In the case of an increase in temperature, a temperature of a material forming a heat receiving tube of the heat receiver is extremely close to the allowable temperature due to the high-temperature heat carrier, and a temperature of the heat receiver is locally different, which causes a problem such that the heat collecting operation cannot be reliably performed.
An outline of a known tower-type heat receiver will be described with reference to FIGS. 10 to 17.
As shown in FIG. 11, a tower-type heat receiver 52 for collecting the sunlight and heat in all areas is developed in accordance with the arrangement of heliostats 50 provided in all areas of 360 degrees in the periphery of a tower 51 shown in FIG. 10. However, since heat receiving tubes 53 are exposed to the outside, a problem arises in that the convection and radiation heat losses are large. For this reason, as shown in FIG. 12, a cavity heat receiver 55 having the heat receiving tubes 53 inside a casing 54 is developed.
In the arrangement of the heliostats provided in all areas in the periphery of the tower, since the effective areas of the mirrors are largely different in the southern and northern areas in accordance with the degree of the incident and reflection angles of the heliostats in the actual facility installation condition in the subtropical high-pressure belt having satisfactory solar radiation, a problem arises in that the effective areas of the mirrors in one of the southern and northern areas are poor.
For this reason, in recent years, as shown in FIG. 13, a heat receiver 61 of a so-called one-side arrangement type has been constructed in which the heliostats 60 are intensively arranged in an area where the effective areas of the mirrors are large in accordance with an actual variation in altitude of the sun. As shown in FIG. 14, the heat receiver 61 has a structure in which the heat receiving tubes 62 are arranged in a curve surface or a substantially polygonal surface within an angular range equal to or less than 180 degrees of the radius in a plan view. In the heat receiver 61, since the height direction of the heat receiving tube is aligned in the horizontal direction, the actual light receiving distribution is high at the center of the heat receiver body in the height direction, and hence there is a tendency that the thermal load of a part of the heat receiving tubes 62 increases. Further, as shown in FIG. 15, the front surfaces of the heat receiving tubes 62 are opened to the outside so as to receive the incident sunlight (the opening is denoted by the reference numeral 63).
Meanwhile, there is known a technology in the Patent Document. A solar heat collector 70 disclosed in the Patent Document 1 is shown in FIGS. 16 and 17. FIG. 17 is a sectional view taken along the line XVI-XVI in FIG. 16. As shown in FIG. 17, there is provided a heat collector 74 including a spirally wound heat carrier circulation tube 73 (heat-exchange heat receiving tube) in which a heat carrier is circulated through a heat carrier introduction portion 71 and a heat carrier extraction portion 72, where a light receiving surface 75 of the heat collector is formed by the outer peripheral surface of the heat carrier circulation tube 73 exposed to the inside of the heat collector.
In addition, the heat carrier introduction portion 71 is provided in the center of the heat carrier circulation tube 73, and the heat carrier extraction portion 72 is provided in the outer periphery of the heat carrier circulation tube 73. Accordingly, the heat carrier inside the heat carrier circulation tube 73 is circulated from the center of the spiral shape to the outer periphery thereof. In addition, the light receiving surface 75 of the heat collector 74 is formed in a curve shape converged toward a sunlight introduction opening.